Transient Receptor Potential (TRP) channels are one of the largest group of ion channels and, based on their sequence homology, are classified into 6 sub-families (TRPV, TRPM; TRPA, TRPC, TRPP and TRPML). TRP channels are cation-selective channels activated by several physical (such as temperature, osmolarity and mechanical stimuli) and chemical stimuli. TRPM8, which was cloned in 2002, is a non-selective cation channel of the TRP family expressed on a subpopulation of somatic sensory nerves on dorsal root ganglion and trigeminal ganglia that causes sensory nerve excitation. It is activated by mild cold temperatures and synthetic cool-mimetic compounds such as menthol, eucalyptol and icilin [McKemy D. D. et al., Nature (2002) 416, 52-58; Peier A. M. et al. Cell (2002) 108, 705-715]. Like several other TRP channels, TRPM8 is also gated by voltage [Nilius B. et al., J. Physiol. (2005) 567, 35-44]. The voltage dependence of TRPM8 is characterized by a strong outward rectification at depolarized transmembrane potential and a rapid and potential-dependent closure at negative membrane potentials. Cooling agents and menthol application shifts the activation curve towards more negative potentials, increasing the possibility for the opening of the channel and boosting inward currents at physiological membrane potentials. Other endogenous factors, such as phospholipase A2 products [Vanden Abeele F. et al., J. Biol. Chem. (2006) 281, 40174-40182], endocannabinoids [De Petrocellis L. et al., Exp. Cell. Res. (2007) 313, 1911-1920] and PIP2 [Rohacs T. et al., Nat. Neurosci. (2005) 8, 626-634] also participate in channel regulation.
There is a lot of direct and indirect evidence of a pivotal role of TRPM8 channel activity in diseases such as pain, ischemia and itch, irritable bowel diseases, cold induced and/or exhacerbated respiratory disorders. Further, it has been demonstrated that TRP channels transduce reflex signals that are involved in the overactive bladder of patients with damaged or abnormal spinal reflex pathways [De Groat W. C. et al., Urology (1997) 50, 36-52]. TRPM8 is activated by temperatures between 8° C. and 28° C. and expressed on the primary nociceptive neurons, including bladder urothelium, dorsal root ganglia, A-delta and C-fibers. The intravesical ice water or menthol also induce C-fiber mediated spinal micturition reflex in patients with urgency and urinary incontinence [Everaerts W. et al., Neurol. Urodyn. (2008) 27, 264-73].
Furthermore, TRPM8 is known to regulate Ca2+ concentration influxes in response to cold temperature or pharmacological stimuli. Finally, in a recent paper, the potential role of TRPM8 in cold-induced asthma and in asthma exacerbation has been proposed, suggesting TRPM8 also a relevant target for the management of these pathologies [Xing H. et al., Molecular Pain (2008), 4, 22-30].
The expression of the channel in brain, lung, bladder, gastrointestinal tract, blood vessels, prostate and immune cells provide further possibility for therapeutic modulation of the activity of TRPM8 in a wide range of pathologies. In particular, the disorders or diseases that have been proven to be affected by the modulation of TRPM8 are pain such as chronic pain, neuropathic pain including cold allodynia and diabetic neuropathy, postoperative pain, osteoarthritic pain, rheumatoid arthritic pain, cancer pain, neuralgia, neuropathies, algesia, fibromyalgia, nerve injury, migraine, headaches; ischaemia, neurodegeneration, stroke, psychiatric disorders, including anxiety and depression, and itch, irritable bowel diseases, cold induced and/or exhacerbated respiratory disorders such as cold induced and/or exhacerbated pulmonary hypertension, asthma and COPD; urological disorders such as painful bladder syndrome, interstitial cystitis, detrusor overactivity (overactive bladder), urinary incontinence, neurogenic detrusor overactivity (detrusor hyperflexia), idiopathic detrusor overactivity (detrusor instability), benign prostatic hyperplasia, lower urinary tract disorders and lower urinary tract symptoms [Nilius B. et al. Science STKE (2005), 295, re8; Voets T. et al., Nat. Chem. Biol. (2005), 1, 85-92; Mukerji G. et al., Urology (2006), 6, 31-36; Lazzeri M. et al., Ther. Adv. Urol. (2009), 1, 33-42; Nilius B. et al., Biochim. Biophys. Acta (2007), 1772, 805-12; Wissenbach U. et al., Biol. Cell. (2004), 96, 47-54; Nilius B. et al., Physiol. Rev. (2007), 87, 165-217; Proudfoot C. J. et al., Curr. Biol. (2006), 16, 1591-1605].
Along the last few years, several classes of non peptide TRPM8 antagonists have been disclosed. WO 2006/040136, WO 2007/017092, WO 2007/017093, WO 2007/017094, and WO 2007/080109 describe benzyloxy derivatives as TRPM8 antagonists for the treatment of urological disorders; WO 2007/134107 describes phosphorous-bearing compounds as TRPM8 antagonists for the treatment of TRPM8-related disorders; WO 2009/012430 describes sulfonamides for the treatment of diseases associated with TRPM8; WO 2010/103381 describes the use of spirocyclic piperidine derivatives as TRPM8 modulators in prevention or treatment of TRPM8-related disorders or diseases; WO 2010/125831 describes sulfamoyl benzoic acid derivatives as modulators of the TRPM8 receptor and their use in the treatment of inflammatory, pain and urological disorders; and WO 2013/092711 describes 2-aryl oxazole and thiazole derivatives as TRPM8 receptor modulators and their use in prevention, reduction of the risk of, amelioration and/or treatment of urological-related disorders.
A therapeutic area in which there is still a particularly high need for the development of antagonists of TRPM8 is that of urological disorders and associated pain. In fact, traditional drugs and medications currently available for the treatment of urinary incontinence and disorders are characterized by several side effects. For example, at the moment, the therapy of overactive bladder syndrome is based on the use of drugs, especially anticholinergic agents that affect peripheral neural control mechanisms or bladder detrusor smooth muscle contraction. These drugs inhibit parasympathetic nerves exerting a direct spasmolytic effect on the muscle of the bladder. The result of this action is the decrease of intravesicular pressure, an increase in capacity and a reduction in the frequency of bladder contraction. However, the use of anticholinergic agents is associated with serious side effects, such as dry mouth, abnormal visions, constipation and CNS disturbances, that impair the overall patient compliance. The inadequacies of the actual therapies highlight the need for novel, efficacious and safe drugs with fewer side effects.